Method for the drilling, in particular percussion or rotary percussion drilling, of holes in soil or rock material and device therefor

ABSTRACT

In a method for drilling holes in soil or rock material, wherein a borehole is formed by a drill bit by a percussive and/or rotational movement, a casing adjoining the drill bit is introduced into the borehole and material that is removed is introduced into the annular space formed between the outer circumference of the drill rod and the inner circumference of the casing via at least one passage opening formed between the drill bit and the casing, and is discharged from the borehole, the impact energy of the drill rod is applied to the drill bit via an adapter cooperating with the drill bit and a drill rod, and that the impact energy is applied to the drill bit partially via an impact shoulder of the adapter and partially via a threaded connection between the adapter and the drill bit.

The present invention relates to a method for drilling, in particular percussion or rotary percussion drilling, holes in soil or rock material, wherein a borehole is formed by a drill bit mounted on a drill rod assembly by a percussive and/or rotational movement, a casing adjoining the drill bit is introduced into the borehole by being pulled and/or struck, and material that is removed is introduced into the annular space formed between the outer circumference of the drill rod assembly and the inner circumference of the casing via at least one passage opening formed between the drill bit and the casing, and is discharged from the borehole. The invention further relates to a device for drilling, in particular percussion or rotary percussion drilling, holes in soil or rock material, wherein a borehole is formed by a drill bit mounted on a drill rod assembly by a percussive and/or rotational movement, a casing adjoining the drill bit is introducible into the borehole by pulling and/or striking, and removed material is introducible into the annular space formed between the outer circumference of the drill rod assembly and the inner circumference of the casing via at least one passage opening formed between the drill bit and the casing, and is dischargeable from the borehole.

For the production of holes in soil or rock material by percussion or rotary percussion drilling, the impact energy, by the aid of a drill bit mounted on a drill rod assembly, is applied to the drill bit either directly via the drill rod assembly or via complex devices like impact shoes, while additionally introducing into the borehole a jacket tube or casing to provide an optionally required further lining, or safely prevent the breaking in of material.

The selection of the drill bit to be employed, of the drill rod assembly and of the casing, which is either pulled along or driven in, depends on the soil or rock material to be removed, and on whether the hole formed in the soil or rock material is to be subsequently used for receiving a rock bolt, forming a pipe roof or even draining the soil or rock material, as well as on the soil or rock material and, in particular, its hardness, stratification, yet even on whether such soil or rock material comprises inclusions like mountain water or the like, wherein the most diverse elements such as drill bits, drill rod assemblies and, in particular, different casings will frequently have to be employed on one and the same construction site.

The present invention aims to further develop a method and a device of the initially defined kind to the effect that an adaptation to the most different subsoil conditions will rapidly and reliably become possible, and that any combination of the elements employed will be freely selectable and usable directly at place as a function of the respective requirements when drilling holes in soil or rock material. It is a further object of the invention to keep the number of different prefabricated devices for drilling holes as low as possible.

To solve these objects, a method of the initially defined kind is essentially characterized in that the impact energy of the drill rod assembly is applied to the drill bit via an adapter cooperating with the drill bit and the drill rod assembly, and that the impact energy is applied to the drill bit at least partially via an impact shoulder of the adapter and at least partially via a threaded connection between the adapter and the drill bit. In that the impact energy of the drill rod assembly is applied to the drill bit via an adapter cooperating with the drill bit and the drill rod assembly, it has become possible in a simple manner to conduct the method according to the invention in such a manner a to enable the respectively most suitable elements to be used as a function of the existing mining or subsoil conditions. In that the method according to the invention is further conducted such that the impact energy is applied to the drill bit at least partially via an impact shoulder of the adapter and at least partially via a threaded connection between the adapter and the drill bit, it is, on the one hand, possible to ensure the safe and reliable transmission of the impact energy onto the drill bit, and it will, on the other hand, be safeguarded that the threaded connection provided for connecting the drill bit with the adapter will not be knocked out during the drilling operation, and hence eventually render impossible the loosening of the connection between the drill bit and the adapter after having completed the drilling operation.

In order to ensure that, in particular after the completion of the drilling operation, the adapter can be separated from the drill bit without damaging any of the components, the method according to the invention is preferably conducted in such a manner that the adapter is coupled to the drill bit by screwing via a quick-acting screw thread connection. In that the adapter is coupled to the drill bit by screwing via a quick-acting screw thread connection, it will, in particular, be ensured that the threaded connection will be safely and reliably undone, and the drill rod assembly together with the adapter will be removed from the borehole, after having completed the drilling operation and, in particular, after having subjected the threaded connection of the adapter with the drill bit to the high stress caused by the introduction of the impact energy. It will, furthermore, be ensured that the adapter will be reusable several times, which will involve considerable economic advantages.

Such a configuration, if required, will additionally enable, during the drilling of holes in soil or rock material, the complete exchange of a drill rod assembly, for instance due to excessive load or wear or defects on the drill rod assembly, or if the subsoil conditions, for instance, call for the use of more stable rods.

In order to ensure that an unintentional detachment of the drill rod assembly from the adapter is prevented during the drilling of holes in rock or soil material, the method according to the invention is preferably further developed to the effect that the adapter is coupled to the drill rod assembly by screwing via a thread, in particular a thread having a smaller pitch than the threaded connection between the drill bit and the adapter. Such a configuration of the method according to the invention ensures that, in particular during drilling, the drill rod assembly plus adapter can be removed from the borehole without inadvertent detachment of the connection between the drill rod assembly and the adapter, so as to be able to perform possibly required adaptation operations.

In order to ensure that drilling debris formed during the drilling of holes will be removed without clogging any openings of the drill bit, the method according to the invention is preferably further developed to the effect that flushing fluid is discharged during drilling through the tubular adapter and through cooperating openings provided in the drill bit. In that the method according to the invention is conducted such that, during drilling, flushing fluid is discharged through the tubular adapter and through cooperating openings provided in the drill bit, it is feasible to supply sufficient flushing fluid volume during drilling by the aid of a structurally simple device both to the working face and optionally also directly to an end region of a drill bit, which end region faces away from the interior of the borehole, or into an annular space provided between the drill bit and a casing, in order to prevent the obstruction of openings and passages by drill debris and also to ensure that an excessive loss of flushing fluid will be avoided during drilling.

In order to, in particular, prevent the discharge of an excessive amount of flushing fluid during the drilling operation, the invention is further developed to the effect that flushing fluid is intermittently discharged during an engagement of the drill bit with the soil or rock material via a flush valve disposed in the adapter and controlled as a function of said engagement. By the intermittent activation of an engagement-controlled flush valve during the engagement of the drill bit with the soil and rock material, an excessive discharge of fluid, or an excessive amount of fluid introduced into the borehole through the flush opening of the drill bit, will, on the one hand, be safely avoided while, on the other hand, simultaneously ensuring that sufficient fluid volume will be available in the interior of the borehole for removing the drill debris.

In order to safely and reliable carry along and, in particular, pull along a casing into the interior of the borehole simultaneously with the formation of a hole in soil and rock material, the method according to the invention is preferably further developed to the effect that the impact energy, in addition, is at least partially applied to the casing via an impact shoulder formed on the drill bit. In that, during the method for drilling holes in soil and rock material, a portion of the impact energy is additionally applied to the casing via an impact shoulder formed on the drill bit, the safe and reliable entrainment of the casing into the interior of the borehole will be safeguarded.

To solve the initially mentioned objects, a device for drilling, in particular percussion or rotary percussion drilling, soil or rock material of the initially defined kind is essentially characterized in that an adapter cooperating with the drill rod assembly and the drill bit is provided, and that the adapter cooperates with the drill bit via an impact shoulder of the adapter and via a threaded connection provided between the adapter and the drill bit. In that a universally applicable adapter cooperating with the drill rod assembly and the drill bit is provided, it has become possible to both freely select the drill bit and the drill rod assembly in adaptation to the requirements encountered during the formation of a hole in soil and rock material and to combine respectively appropriate elements with one another. In that the adapter is configured such that the adapter cooperates with the drill bit via an impact shoulder of the adapter and via a threaded connection between the adapter and the drill bit, it will be ensured that, on the one hand, the drilling energy will be safely and reliably transmitted to the drill bit and, on the other hand, the threaded connection between the adapter and the drill bit, which is susceptible to knocking out or damage, will be stressed as little as possible.

In that, as in correspondence with a preferred further development of the device according to the present invention, the adapter is coupled to the drill bit via a quick-acting screw thread connection, a force distribution will be achieved in such a manner as to safely prevent damage to the threaded connection, on the one hand, and to ensure that, during the separation of the adapter and the drill rod assembly from the drill bit, the connection between the drill bit and the adapter will be readily and reliable undone, in particular prior to the detachment of other optionally provided threads, on the other hand.

Such a threaded connection can, for instance, be configured as a quick-acting screw thread connection having two turns, by which both a safe and reliable retention of the adapter within the drill bit will be ensured and an intended detachment of the adapter from the drill bit will be achieved.

In that, as in correspondence with a preferred further development of the present invention, the device is configured such that the adapter is coupled to the drill rod assembly via a further thread having a pitch differing from that of the thread connection between the adapter and the drill bit and, in particular, a smaller pitch, it has become possible to safely prevent any inadvertent detachment of the adapter from the drill rod assembly both during the drilling operation and while screwing the adapter out of the drill bit. Such a configuration, moreover, ensures that at least the drill rod assembly and the adapter will be recoverable without damage at the end of the drilling procedure, thus achieving considerable cost savings.

In that, as in correspondence with a preferred further development of the present invention, the device is configured such that the end face of the adapter facing the interior of the borehole is designed to be at least partially chamfered, it has become possible to safely insert the adapter, which is coupled to the drill rod assembly, together with the drill rod assembly into the drill bit and connect the same by screwing, in particular where maintenance operations are required during the formation of the borehole, so as to enable adaptation work to be performed on the drill rod assembly even in case of, for instance, half-finished holes.

For the reliable introduction of flushing fluid into the interior of the borehole, the invention is preferably further developed to the effect that the tubular adapter is formed with a passage opening for flushing fluid facing the interior of the borehole, and that the passage opening cooperates with openings for discharging flushing fluid, that are provided in the drill bit. By such a device, it will be ensured that flushing fluid will be introduced into the flush openings formed in the drill bit through the hollowly designed adapter and will be available in the interior of the borehole for the drilling operation and, optionally, in the annular space between the drill bit and the casing such that, on the one hand, the removal of drill debris will be effected through openings or recesses formed in the drill bit in a known manner and, on the other hand, clogging of the openings for both the flushing fluid and the evacuation of drill debris in the drill bit and/or, optionally, in the annular space or annular gap will be prevented.

According to a further development of the invention, the device is configured such that an engagement-controlled flush valve is provided in the adapter. By providing an engagement-controlled flush valve in the adapter, the controlled discharge of flushing fluid through the adapter and through the flush openings formed in the drill bit has become possible such that, on the one hand, only those amounts of flushing fluid which are required for the proper removal of drill debris will be discharged and, on the one hand, an obstruction of the openings, in particular the flush opening, by drill debris will be prevented. The engagement-controlled flush valve can be formed via a pressure switch or pressure valve provided in the said annular space.

In order to be able to utilize the drilling energy introduced through the adapter, in particular, also for pulling along a casing, and to safely and reliably apply the impact energy also to a casing, the device according to the invention is further developed to the effect that the drill bit comprises at least one impact shoulder for cooperating with the casing and, in particular, applying an impact stress on the casing. Such a configuration will ensure that the casing will be subjected to an impact stress also in its front end region during the application of an impact stress on the drill bit so as to be able to be introduced into the borehole without being driven in from outside. The casing will thus be pulled into the interior of the borehole by the impact stress exerted on its front end region.

In that, as in correspondence with a preferred further development of the present invention, the casing is configured such that it is designed to be thickened in its end region facing the interior of the borehole and the thickened portion, in its end region facing away from the interior of the borehole, is designed complementary to an impact shoulder of the drill bit, the cooperation of the complementarily designed impact shoulder of the drill bit with the thickened region of the casing will ensure the reliable striking-in or introduction of the casing into the borehole.

Due to such a configuration, any casing that appears suitable for the drilling procedure to be expected, e.g. an expandable casing, can, for instance, be disposed in a drill bit end region facing away from the interior of the borehole prior to the start of a drilling procedure, and subsequently fixed to the drill bit by pressing, in particular in such a manner that the casing will be non-detachably connected with the drill bit so as to be longitudinally displaceable along the drill bit. Since the thickened portion of the casing, in its end region facing away from the interior of the borehole, comes into abutment on the impact shoulder of the drill bit as the drill bit is being struck into the borehole, in particular during the application of impact stress, the reliable entrainment of the casing into the borehole will be ensured. In the event that, during the drilling operation, a displacement of the casing is no longer possible, in particular in the region where the casing is disposed to be longitudinally displaceable along the drill bit, the free movement of the casing within the borehole can, for instance, be restored by exerting an impact stress from outside.

In that, as in correspondence with a preferred further development of the present invention, the device is further devised such that the end region of the casing facing the interior of the borehole is designed with a depression, in particular an asymmetrically shaped depression, the drill bit can be thrown off the casing, thus enabling the separation of the drill bit from the casing and, for instance in the event of a dividedly designed drill bit, the recovery from the borehole of at least part of the drill bit together with the drill rod assembly and the adapter, after having completed the drilling process.

In the following, the invention will be explained in more detail by way of exemplary embodiments illustrated in the drawing. Therein:

FIG. 1 depicts a section through the device according to the invention for carrying out the method of the invention for drilling holes;

FIG. 2 is a partially perspective external view of the device according to FIG. 1;

FIG. 3 is a longitudinal section through a variant of the adapter of FIG. 1;

FIG. 4 depicts a longitudinal section through a modified variant of the adapter according to the invention; and

FIG. 5 depicts a section through the end region facing the interior of the borehole, of a variant of the casing of the device according to the invention for drilling holes.

From FIG. 1, it is apparent that a device for drilling or rotary percussion drilling holes in soil or rock material, which is generally denoted by 1, comprises a drill bit schematically indicated by 2, which, via an adapter 3, is connected to a drill rod assembly 4 schematically indicated in FIG. 1.

Furthermore, the drill bit 2 is adjoined by a casing 5 whose end region 6 facing the interior of the borehole has a thickness that is enlarged relative to the region of the casing 5 facing the exterior of the borehole. Said end region 6, in its end region 7 facing away from the interior of the borehole, is chamfered and has a shape complementary to an impact shoulder 8 of the drill bit 2. This configuration causes at least a portion of the impact energy to be applied to the chamfer 7 via the impact shoulder 8 during the drilling of holes such that the casing 5 will be entrained into the borehole 1 as drilling proceeds.

The drill bit 2 is connected to the adapter 3 by a thread schematically indicated by 9, wherein an annular space 10 is formed above the end of the adapter 3 facing the borehole and the drill bit 2, via which annular space 10 flushing fluid can be discharged towards the interior of the borehole through a flushing fluid channel 11 provided in the interior of the hollowly designed adapter 3 and through holes 12 provided in the drill bit 2 for the passage of flushing fluid.

The drilling energy applied to the adapter 3 via the drill rod assembly 4 in the configuration according to FIG. 1 is applied to the drill bit 2 via an impact shoulder 13, on the one hand, and partially via the thread 9, on the other hand. Such a configuration ensures that the thread 9 will not be excessively stressed during the drilling operation and, in particular, will not be knocked out so as to enable the safe and reliable separation of the adapter 3 from the drill bit 2 after the drilling operation has been completed.

The drill bit 2 illustrated in FIG. 1 is a conventional drill bit designed in one piece, which includes a plurality of drill pins 14 and also recesses 15 beside the openings for discharging flushing fluid 12, via which recesses drill debris can be introduced into the annular space 17 provided between the adapter 3 or the drill rod assembly 4 and the casing 5 through recesses 16 formed between the casing 5 and the drill bit 2, and can subsequently be discharged from the borehole exterior. In order to prevent the annular space 17 from being clogged by drill debris, the drill bit 2, moreover, comprises a backwardly directed flushing channel 27 via which the annular space 17 can be sufficiently rinsed.

In the illustration according to FIG. 2, the reference numerals of FIG. 1 have been retained, wherein it is apparent from the illustration according to FIG. 2 that the casing 5, in its end region 6 facing the interior of the borehole has a diameter that is reduced relative to that of the region facing the borehole exterior, which diameter reduction can be readily achieved by pressing the casing 5 onto a drill bit 2, so that, prior to the start of a drilling operation, any combination comprising a drill bit 2, an adapter 3, a drill rod assembly 4 and a casing 5 can be composed as a function of the requirements to be expected, thus providing an extremely simple and cost-effective variant of a device for drilling holes in soil and rock material. Needless to say that the casing 5 in this variant may be any desired casing as is employed during the drilling of holes in soil and rock material, such as a frictionally engaged casing, an expandable casing, a drain pipe or, for instance, even a casing allowing for a certain mobility of the individual segments forming the casing and capable of following deviations from the drilling direction to a certain extent.

Also the drill bit 2 used in this context can be arbitrarily selected in deviation of the illustrations according to FIGS. 1 and 2, wherein, in addition to a drill bit designed in one piece, a drill bit comprised of several parts, of which, for instance, only one part will remain in the interior of the borehole after the completion of the drilling process, an asymmetrically designed drill bit, and a drill bit comprising cutters instead of drill pins can be used.

FIG. 2, furthermore, schematically depicts an asymmetrically designed depression 19 provided on the upper edge 18 of the casing 5 that faces the interior of the borehole, which depression 19 comprises a vertical or steeply formed side cheek and a less sloped second cheek 20, such a depression, for instance, enabling the drill bit 2 to be thrown off after the completion of the drilling operation.

FIG. 3 illustrates a variant of the adapter 3 of FIG. 1, said adapter again having a thread 9 on its end region to be coupled to the drill bit 2. The thread 9 of the adapter 3 is configured as a quick-acting screw thread having two turns, in order to ensure a safe and reliable connection of the adapter 3 with the drill bit 2 during the drilling operation, and to enable the separation of the adapter 3 from the drill bit 2 after the completion of the drilling operation in such a manner that the connection between the drill bit 2 and the adapter will be that connection of the whole device 1 for drilling holes in soil or rock material which will come loose first when stressed accordingly.

Beside the passage channel 11 for flushing fluid, which is again schematically indicated, a further thread 21 is provided in the interior of the hollowly designed adapter 3, in its region facing the exterior of the borehole, for connection to a drill rod assembly 4, said thread 21 having, on the one hand, significantly more turns and, on the other hand, a significantly smaller pitch than the thread 9 in order to safely prevent any inadvertent loosening of the connection of the adapter 3 with the drill rod assembly, in particular after the completion of a drilling operation.

In the variant of FIG. 3, the impact shoulder 13 of the adapter 3, unlike in the illustration according to FIG. 1, is chamfered in order enable an even better application of the impact energy to the drill bit 2, wherein the wear of the impact shoulder 13 will, in particular, be clearly reduced with a chamfered impact shoulder 13.

In the variant according to FIG. 3, the end region 22 of the adapter 3 facing the interior of the borehole is, moreover, provided with chamfers 23 to facilitate the insertion or threading of the adapter 3 into a drill bit 2, which will be of particular advantage when replacing the drill rod assembly during a drilling operation.

In the illustration of FIG. 4, which is substantially identical to that of FIG. 3, the adapter 3 also comprises a quick-acting screw thread 9 for the insertion of the adapter 3 into a drill bit 2, as well as a further thread 21, which has a significantly reduced pitch and a significantly increased number of turns relative to thread 9. The impact shoulder 13, as in the illustration of FIG. 3, is, moreover, chamfered, with a chamfer 23 being formed on the end face 22 of the adapter 3 facing the interior of the borehole.

Unlike in the illustration according to FIG. 3, the variant according to FIG. 4 comprises a pressure switch 24 provided on the end face 22, via which pressure switch 24 an intermittently openable valve 25 is provided, which is schematically indicated in the passage 11 for discharging flushing fluid. During the drilling operation, the pressure switch 24 is actuated by pressurization at said drilling operation, whereupon the valve 25 is opened and flushing fluid is either discharged directly through openings for flushing fluid 12 provided in the drill bit, or is discharged towards the interior of the borehole via the annular space 10 provided between the drill bit 2 and the adapter 3 and through the opening for flushing fluid 12. Such a configuration safeguards that an excessive consumption of flushing fluid will be avoided during the drilling operation while, at the same time, ensuring that the usually extremely small openings for flushing fluid formed in the drill bit will not be clogged by drill debris during the drilling operation.

With reference to the adapter 3, it is noted that its external dimensions such as, e.g. its threads 9 and 21, are designed to suit all current drill bits 2 and drill rod assemblies 4 such that the adapter 3 constitutes a universally usable element whose use does, moreover, not require any conventionally employed auxiliary equipment such as impact shoes, special connection sleeves for connecting the drill bit to the drill rod assembly, and the like, the use of the adapter 3 according to the present invention thus providing a simplified and economically favorable and universally usable device for drilling holes in soil or rock material.

In the illustration according to FIG. 5, a section, in particular a longitudinal section, through the end region of a casing 5 facing the interior of the borehole is shown, said end region 6 of the casing 5 facing the interior of the borehole being again thickened. At the transition from the thickened end region 6 to the portion of the casing 5 facing the exterior of the borehole, a shoulder 7 is again provided to cooperate with a shoulder 8 of a drill bit 2 so as to enable the casing 5 to be pulled into the interior of the borehole.

In the illustration according to FIG. 5, the depression 19 is shown in the edge region 18 of the casing 5 facing the interior of the borehole, wherein the side cheek 20 of the depression 19 is designed to extend to the edge 18 with a small gradient. The second side cheek 26 of the depression 19 is designed to extend normally to the edge 18, which variant makes it possible to throw off a drill bit 2 by a slight turn of the casing 5 upon completion of the drilling procedure in order to either recover the drill bit 2 at least partially or continue the drilling procedure without carrying along a casing 5.

In that the casing 5 is pressed on the drill bit 2 in a manner mounted to be displaceable in the longitudinal direction of the drill bit 2, as can be taken from the illustration according to FIG. 1, an impact energy can be additionally applied to the casing 5 from the exterior of the borehole, if required, in order to make possible also the driving-in of the casing 5 in addition to the pulling-in of the casing 5 via the coupling provided between the impact shoulder 8, the drill bit 2 and the shoulder 7 of the casing 5. Such driving-in of the casing 5 may be necessary in some cases such as, e.g. when the passage gap 16 between the drill bit 2 and the casing is clogged by drill debris, or when further pulling along of the casing 5 by the drill bit 2 [is not possible]_(sic) due to broken-in material filling the space between the edge 18 of the casing 5 and a respective portion of the drill bit 2 surmounting the casing 5 or terminating flush with the same. 

1. A method for drilling, in particular percussion or rotary percussion drilling, holes in soil or rock material, wherein a borehole is formed by a drill bit mounted on a drill rod assembly by a percussive and/or rotational movement, a casing adjoining the drill bit is introduced into the borehole by being pulled and/or struck, and material that is removed is introduced into the annular space formed between the outer circumference of the drill rod assembly and the inner circumference of the casing via at least one passage opening formed between the drill bit and the casing, and is discharged from the borehole, wherein that the impact energy of the drill rod assembly is applied to the drill bit via an adapter cooperating with the drill bit and the drill rod assembly, and that the impact energy is applied to the drill bit at least partially via an impact shoulder of the adapter and at least partially via a threaded connection between the adapter and the drill bit.
 2. The method according to claim 1, wherein that the adapter is coupled to the drill bit by screwing via a quick-acting screw thread connection.
 3. The method according to claim 1, wherein that the adapter is coupled to the drill rod assembly by screwing via a thread, in particular a thread having a smaller pitch than the threaded connection between the drill bit and the adapter.
 4. The method according to claim 1, wherein that flushing fluid is discharged during drilling through the tubular adapter and through cooperating openings provided in the drill bit.
 5. The method according to claim 4, wherein that flushing fluid is intermittently discharged during an engagement of the drill bit with the soil or rock material via a flush valve disposed in the adapter and controlled as a function of said engagement.
 6. The method according to claim 1, wherein that the impact energy, in addition, is at least partially applied to the casing via an impact shoulder formed on the drill bit.
 7. A device for drilling, in particular percussion or rotary percussion drilling, holes in soil or rock material, wherein a borehole is formed by a drill bit mounted on a drill rod assembly by a percussive and/or rotational movement, a casing adjoining the drill bit is introducible into the borehole by pulling and/or striking, and removed material is introducible into an annular space formed between the outer circumference of the drill rod assembly and the inner circumference of the casing via at least one passage opening formed between the drill bit and the casing, and is dischargeable from the borehole, wherein that an adapter cooperating with the drill rod assembly and the drill bit is provided, and that the adapter cooperates with the drill bit via an impact shoulder of the adapter and via a threaded connection provided between the adapter and the drill bit.
 8. The device according to claim 7, wherein that the adapter is coupled to the drill bit via a quick-acting screw thread connection.
 9. The device according to claim 7, wherein that the adapter is coupled to the drill rod assembly via a further thread having a pitch differing from that of the thread connection between the adapter and the drill bit, in particular a smaller pitch.
 10. The device according to claim 7, wherein the end face of the adapter facing the interior of the borehole is designed to be at least partially chamfered.
 11. The device according to claim 7, wherein the tubular adapter is formed with a passage opening for flushing fluid facing the interior of the borehole, and that the passage opening cooperates with openings for discharging flushing fluid, that are provided in the drill bit.
 12. The device according to claim 7, wherein an engagement-controlled flush valve is provided in the adapter.
 13. The device according to claim 7, wherein the drill bit comprises at least one impact shoulder for cooperating with the casing and, in particular, applying an impact stress on the casing.
 14. The device according to claim 7, wherein the casing is thickened in its end region facing the interior of the borehole and the thickened portion, in its end region facing away from the interior of the borehole, is designed complementary to an impact shoulder of the drill bit.
 15. The device according to claim 7, wherein the end region of the casing facing the interior of the borehole is designed with a depression, in particular an asymmetrically shaped depression. 